Electroencepholographic recordings from the human brain reveal complicated waveforms - often oscillatory - with energy in many different frequency bands. This activity (e.g., the energy of 40 Hz signals) is usually state-dependent and varies with the subject's attentiveness or wakefulness. Some of the most dramatic modulations occur in the different phases of sleep. These macroscopic signals generally represent the synchronized activity of large numbers of neurons that fire periodically and occur in all mammals, non-mammalian vertebrates and smaller animals such as insects and molluscs. The functional relevance of these signals -thus, of the signals that cause them-remains, however, largely conjectural. The present work is directed at deciphering some of these neural, distributed and coordinated phenomena and at providing a functional and computational understanding of their existence. The approach exploits the accessibility of small nervous systems (insect brains) and the prevalence of such coordinated phenomena in olfactory circuits (insect olfactory system: antennal lobe and mushroom bodies). The methods used are electrophysiological (intracellular and multi-single unit recordings) and computational (quantitative analysis, simulations). Because olfactory circuits in insects and mammals are so alike, the potential payoff of this work is a better understanding of neural coding, olfactory representations and of the format of memories in brain circuits in general. For example, the fundamental problem of representation sparsity (i.e., whether a memory should be represented by a large or small subset of a neural assembly) can be studied directly in ways that are impossible today with the large brains of mammals. This work will thus have relevance to present efforts to decipher memory circuits in rodents and primates and coding strategies used by the human brain. [unreadable] [unreadable]